[?] Subscribe To
There are a variety of different materials that a biodiesel reactor can be made out of. Some of these are :
Either Polyethylene or Polypropylene. Do not use PVC as it's temperature range is not good enough. Cross linked Polyethylene (PEX) is better. The advantage of plastic is that it is cheap while having good chemical resistance. It can also be molded at low cost into conical bottomed tanks which are ideal. If you want a good conical bottom tank look for a Plastic Roto Molding Company near you. A farm CoOp will stock them.
Some people use 44 Gallon Plastic drums for biodiesel processors. These can make good processors. The biggest disadvantage of a drum processor is that because it has a flat bottom it is hard to separate the various layers of liquids properly. There are some large commercial plants that use polyethylene tanks.
The disadvantage of plastic is that it has no fire resistance. If you are going to use plastic for your processor avoid putting an element directly into the side of the tank. It will fail and has a good chance of catching on fire - a biodiesel fire is a serious event. Just about all the plants I have ever been in use polyethylene wash and storage tanks.
Mild steel makes a good biodiesel reactor. It is strong, safe and moderately resistant to the caustic chemicals. It will corrode eventually. Some people use steel and black iron fittings for their processor piping and this is an acceptable solution. The piping will eventually need replacing but this can be planned for. It has the advantage of being cheap and usually readily available. The most common home made biodiesel processor is an appleseed processor which has a steel shell and steel piping. This type of processor is made from a hot water heater.
Any grade of stainless steel from 304 up is perfect for a biodiesel processor. 304 has good resistance to all the chemicals used in biodiesel. The only issue is expense, stainless is very expensive to buy and expensive to fabricate. For this reason home brewers tend to not use it. However if you have access to some second hand tanks they will make a fine biodiesel plant. You should use stainless piping and valves where possible when building a stainless steel plant. You can also use modern multi layered PEX piping which is ideal.
The other reason commercial plants use stainless steel is that because it is chemicaly inert it will not effect the quality of the biodiesel in any way. Steel, copper and other metals will have an effect on the fuel and will reduce its long term properties.
If you look at all the plant photos above you will notice that all of them are raised above the floor. The reason for this is to allow the contents of the tank to gravity feed into the pump. This means that the pump that you select does not have to be self priming which results in a significant saving.
The in feed tank has to be easy to fill. In a small plant this would mean the tank has to be low enough to allow for the oil to be poured in. In a larger plant the oil is usually pumped into large storage tanks which then feed into the biodiesel reactor.
All the above reactors have a sight glass on the side of the vessel. The sight glass shows the volume of oil in the vessel. In our processor schematic the sight glass is between valves 9 and 10. On much larger plants the contents of the vessel are determined by weight.
Most biodiesel reactors have built in heating elements to heat the oil. There are a couple of things to bear in mind when putting a heater into a vessel like this.
Firstly, if you are using plastic for the construction of your vessel, don't put a heater in it! Putting a heating element into a plastic wall is asking for trouble. Rather put an inline heater into the piping that feeds into the vessel. This is a much safer practice.
The heating element that you put into your vessel or into an inline heater should be a low wattage density element. If you approach an element manufacturer and tell him you are heating vegetable oil, they will know exactly what to make for you. The standard elements that are used for heating water should not be used. Google 'Heating Element Manufacturer' to find a manufacturer in your area.
In an appleseed design processor high density elements are often used, one of the reason that people get away with using them is that the appleseed is a sealed vessel. If the oil is overheated there is no oxygen for the oil to catch fire. But it is not good practice.
Personally I like an external, inline heater. It simplifies the construction of the processor and reduces the number of holes that have to be cut into the walls.
All reaction vessels should have an external vent. This is important as you do not want any pressure build up in your vessel. This does mean that your processing temperature is restricted to less than the boiling temperature of methanol which is 64 deg C. The recommended processing temperature for a home biodiesel reactor is 55-60 deg C. This is quite adequate and the biodiesel reaction will happen within two hours.